It was on my car door. I had to wait awhile to use it due to the weather. When I finally applied the substance to the rust,I looked at it the next day and it sort of cleaned it up. I can't really tell.

The stuff works great to remove rust. It will remove some platings and oxide finishes (gun bluing), which is good if you want them removed. It also seems to strip yellow dichromate, so think twice before using on yellow chrome parts (most of my auto machine screws. Grrr.). Generally, you want enough Evaporust to fully immerse your parts. Although it is safe to leave your parts soaking for days, make sure that they are completely covered. I've found that etching can occur at the "water line" for parts that are left half in and half out.